The present invention relates to repair of heat exchangers and the like, and more particularly to a method and apparatus for stabilizing the broken ends of a tube within a tubular heat exchanger, boiler or the like.
In enclosed or tubular type heat exchangers one fluid flows through a bundle of parallel tubes supported by tube sheets at both ends of an outer shell through which another fluid passes. Some designs include winding tubes, or baffles spaced along the length of the shell, to increase heat transfer. Over long periods of usage, the structural integrity of a tube may weaken and fracture due to vibration and thermal contraction and expansion. Rather than shut down operations for an extended period necessary to repair or replace the defective tube, a temporary "quick fix" is preferred which entails removing the end covers or heads and plugging the tube at both ends. Tube replacement is thereby deferred until a future planned shutdown. To minimize the downtime even further, only the cover at one end is removed and a special tool manipulated from the uncovered "near" end of the tube to secure a plug in the enclosed "far" end. For instance, U.S. Pat. No. 4,393,564 entitled "Method and Apparatus for Repairing Heat Exchangers" by John E. Martin, describes a hydraulically-operated plugging tool in which a compression tube and pull rod extend into the defective tube for tightly expanding an attached two-part tapered plug in the far end of the tube adjacent to the tube sheet. When the appropriate force for wedging the plug is applied between the tube and rod, the plug is released allowing the tool to be withdrawn from the tube. The near end of the tube may be similarly plugged using a shorter plugging tool.
Even with the defective tube plugged at both ends as described above, there are situations where the tube completely fractures at a location between the tube sheets or baffles leaving one or both disjoined ends free to vibrate. Fluid turbulence within the shell around the defective tube may then cause the free ends to strike adjacent working tubes in a whip-like motion and thereby exacerbate conditions. An attempt to solve this problem employs a stiff insert or stabilizer rod extended the full length of the defective tube to bridge the gap and immobilize the fractured ends. The stabilizer is secured within the tube by various methods such as by welding, roller expansion and explosive forming. Another method suggests anchoring the stabilizer to the tube by a ram-operated plug such as disclosed in U.S. Pat. No. 4,393,564, supra. However, if the stabilizer rod were to be anchored at both ends of the tube, then both end covers of the shell would have to be removed to install the plugs. On the other hand, if the rod were to be anchored at both ends from only one end of the tube with the above-described plugging tool, then the stabilizer rod would have to be hollow in order to access the far end. Such a requirement would considerably limit the stabilizer rod's strength and stiffness to such an extent that it may not withstand the stresses placed on it during normal heat exchange service. Moreover, a stabilizer rod, whether solid or hollow, if anchored at both ends of the defective tube, may cause untimely fatigue and damage to the tube sheets and adjacent tubes with repeated stresses due to differential expansion from thermal cycling of the heat exchanger.